Online educational resource on achieving indoor environmental quality with radiant based HVAC systems
Not for profit educational resource on indoor environmental quality.
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Table 1 Representative Rates at Which Heat and Moisture Are Given Off by Human Beings in Different States of Activity, Nonresidential Cooling and Heating Load Calculation Procedures, Section 29.4, 2001 ASHRAE Fundamentals Handbook, Copyright  2007, American Society of Heating, Refrigeration and Air-Conditioning Engineers, It is presented for educational purposes only. This table may not be copied and/or distributed electronically or in paper from without permission of ASHRAE

Table 1. Representative Rates at Which Heat and Moisture Are Given Off by Human Beings in Different States of Activity.

Copyright 2007, American Society of Heating, Refrigeration and Air-Conditioning Engineers, It is presented for educational purposes only. This table may not be copied and/or distributed electronically or in paper from without permission of ASHRAE

At rest, over 50% of the sensible heat transfer between the occupant and the room is radiant based - and yet 99.99% of all thermostats measure air temperature - go figure.

Visit our radiant design and performance characteristics page.


Glossary of Terms
Bibliography / resources


For a full overview on building codes and controlling radiant see the inaugural issue of BetterBuildings


For conditioning of air with radiant based HVAC see Dedicated Outside Air Systems (DOAS)


"Due to the density of water, more energy can be captured and channelled with water than air. It is difficult to imagine how or why the body would use air to move heat energy; the size of the respiratory system, the diameter of veins and arteries, and the caloric intake require to thermal condition would be as absurd as it would be inefficient. It is hard, then, to imagine why we design and condition buildings in this way."
Kiel Moe, Assistant Professor, Architectural Technology,
Harvard University

Definition of Radiant Based HVAC Systems:
Copyright (c) 2004 Robert Bean, All rights reserved.

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Radiant based HVAC systems by its implied definition, integrates the interior surface temperatures of the building enclosure for the purposes of evaluating the mean radiant temperature for establishing thermal comfort based on human factor design.

Background: The control over surface temperatures for thermal comfort is not new; to set the bookends as it were, are two quotes one from 1857 and another 2010 - both from internationally recognized authorities on health and buildings advising us to focus on the enclosure to control heat transfer by radiation:

1857 - "the Commissioners of the General Board of Health advocated as one of the requirements for comfort that the walls of a room be at least as high in temperature as the general temperature of the room, while they included cold walls or floors amongst the conditions which make for discomfort.”1

2010 - National Building Code of Canada v2010: Section A-5.3.1.2.(1) Use of Thermal Insulation or Mechanical Systems for Environmental Control states, “In addition to controlling condensation, interior surface temperatures must be warm enough to avoid occupant discomfort due to excessive heat loss by radiation.”

Furthermore, recognized authorities in human factor design and thermal comfort are in agreement with the UK's Health and Safety Executive which states,

“The most commonly used indicator of thermal comfort is air temperature – it is easy to use and most people can relate to it. But although it is an important indicator to take into account, air temperature alone is neither a valid nor an accurate indicator of thermal comfort or thermal stress.”

Introduction:

Many people assume wrongly that Radiant Based HVAC Systems are exclusively mechanical or electrical solutions like floor heating.

radiant energy is the basis for radiant based HVAC systemsHowever, 'radiant' control is ideally first a building science solution.

This means the building enclosure should be the prime solution for controlling the radiant exchange between the occupant and the interior surfaces. 

This is achieved with building efficiency.  The higher the performance in the building enclosure the less temperature difference between the person and the room mass the more likely the conditions for occupants to perceive thermal comfort.  This begins to occur in my experience when loads are reduced with architectural systems to less than approximately 12 Btu/hr/sf.

Mechanical solutions, like low temperature radiant heating and high temperature radiant cooling can then be applied if necessary to compensate for the buildings short comings. 

Therefore, when we use the term Radiant Based HVAC Systems, please understand we are first and foremost talking about the body’s radiant heat transfer to and from the built environment (see Table 1.) and controlling it with architecture then with mechanical solutions.

As illustrated below, low performing buildings using traditional heating systems need high fluid temperatures in heating (and low temperatures in cooling) but only a high performance building can use low temperatures in heating and high temperatures in cooling (applies to all systems). In fact with high performing buildings, using radiant cooling and heating, conductive floors and close tube spacing, fluid and surface temperatures operate close to the core body temperature and enable maximum efficiency from the heating and cooling plant.


click to enlarge

Such a small difference between the fluid temperatures in the pipes and the temperature in your blood has a major benefit in that it greatly enhance the efficiency of chillers, condensing boilers, solar and heat pumps. So you win when you improve the building and you win when you use low temperature radiant heating and high temperature radiant cooling.

Learn about the benefits of using a dedicated outdoor air system (DOAS, i.e. HRV's/ERV's) operating in parallel with radiant cooling and heating systems.

To see an example of a high performance building with radiant heating and HRV's for ventilation click here.

See overview of housing performance categories in North America.


1. Source: Subjective Impressions of Freshness In Relation To Environmental Conditions by T. Bedford, D.Sc., Ph.D. and C. G. Warner, Ph.D., B.Sc., of the Industrial Health Research Board and the London School of Hygiene and Tropical Medicine, 1939
<http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2199495/> accessed Oc. 17, 2011


If you wish to discuss this further please visit the Online Help.

see also: Radiant Based HVAC – What does it mean to indoor air quality?
 

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